JP2011176220A - Wiring board, method of manufacturing wiring board, and via paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board that has interlayer connection by a via hole conductor having high reliability of electric connection, and meets the need for a Pb-free feature. <P>SOLUTION: The wiring board 11 has: a plurality of interconnects 12 arranged with an insulating resin layer 13 interposed; and the via hole conductor 14 electrically connecting the plurality of interconnects 12 to each other. The via hole conductor 14 includes: a metal portion 15; and a resin portion 16, the metal portion 15 includes: copper particles 17; a first metal region 18 containing as a principal component, tin, tin-copper alloy and a tin-copper inter-metal compound; and a second metal region 19 containing as a principal component, bismuth, wherein Cu/Sn is 1.59 to 21.43, the copper particles 17 come in contact with one another to electrically connect the plurality of interconnects 12 to each other, and at least a part of the first metal region 18 covers a periphery of portions where copper particles 17 are in contact with one another. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multilayer wiring board in which a plurality of wirings arranged via an insulating resin layer are electrically connected to each other. Specifically, the present invention relates to an improvement in a via hole conductor for interlayer connection of multilayer wiring.

  Conventionally, there has been known a multilayer wiring board obtained by interlayer connection of wirings arranged via an insulating resin layer. As such an interlayer connection method, a via-hole conductor is known which is formed by filling a hole formed in an insulating resin layer with a conductive paste. Moreover, what filled the metal particle containing Cu instead of the electrically conductive paste and fixed these metal particles with the intermetallic compound is also known.

  Specifically, for example, Patent Document 1 below discloses a via-hole conductor having a matrix domain structure in which domains composed of a plurality of Cu particles are interspersed in a matrix of CuSn compounds.

  Further, for example, Patent Document 2 below discloses a sinterable composition used for forming a via-hole conductor, which includes a high-melting-point particle phase material containing Cu and a low-melting-point material selected from metals such as tin or a tin alloy. is doing. Such sinterable compositions are compositions that are sintered in the presence of a liquid phase or a transient liquid phase.

  Further, for example, in Patent Document 3 below, a solid paste having a solid phase temperature of 250 is formed on the outer periphery of the copper particles by heating a conductive paste containing Sn-Bi metal particles and copper particles at a temperature equal to or higher than the melting point of the Sn-Bi metal particles. A via-hole conductor material in which an alloy layer at a temperature of ° C or higher is formed is disclosed. Such a via-hole conductor material has a high connection reliability since the interlayer connection is performed by joining the alloy layers having a solid phase temperature of 250 ° C. or higher, and the alloy layer does not melt even in a heat cycle test or a reflow resistance test. It is described that it can be obtained.

JP 2000-49460 A Japanese Patent Laid-Open No. 10-7933 JP 2002-94242 A

  The via-hole conductor disclosed in Patent Document 1 will be described in detail with reference to FIG. FIG. 15 is a schematic cross-sectional view of a via hole portion of a wiring board disclosed in Patent Document 1.

In the schematic cross-sectional view of the wiring board in FIG. 15, the via-hole conductor 2 is in contact with the wiring 1 formed on the surface of the wiring board. The via-hole conductor 2 includes a matrix 4 containing Cu ₃ Sn and Cu ₆ Sn ₅ which are intermetallic compounds, and a copper-containing powder 3 interspersed as domains in the matrix 4. In this via-hole conductor 2, a matrix domain structure is formed by setting the weight ratio represented by Sn / (Cu + Sn) in the range of 0.25 to 0.75. However, such a via-hole conductor 2 has a problem that voids and cracks (5 in FIG. 15) are likely to occur in the thermal shock test.

Such voids and cracks are caused by CuSn such as Cu ₃ Sn, Cu ₆ Sn _5, etc., when Cu is diffused into the Sn—Bi-based metal particles when the via-hole conductor 2 receives heat in a thermal shock test or a reflow process. It corresponds to a crack caused by the formation of a compound. In addition, such voids include Cu ₃ Sn, which is an intermetallic compound of Cu and Sn contained in a Cu—Sn diffusion junction formed at the interface between Cu and Sn. This is also caused by the fact that internal stress is generated in the via-hole conductor 2 by changing to Cu ₆ Sn ₅ by heating.

  In addition, the sinterable composition disclosed in Patent Document 2 is sintered in the presence or absence of a transient liquid phase, which occurs during, for example, a hot press for laminating a prepreg. It is a composition. Such a sinterable composition contains Cu, Sn, and Pb, and the temperature during hot pressing is as high as 180 ° C. to 325 ° C., so an ordinary glass fiber is impregnated with an epoxy resin. It was difficult to correspond to an insulating resin layer (sometimes called a glass epoxy resin layer). In addition, it has been difficult to cope with the Pb-free demand required by the market.

  Moreover, in the via-hole conductor material disclosed in Patent Document 3, the alloy layer formed on the surface layer of the copper particles has a high resistance value. Therefore, it becomes a high resistance value compared to a connection resistance value obtained only by contact between Cu particles or between Ag particles like a general conductive paste containing Cu particles, silver (Ag) powder or the like. There was a problem.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a wiring board capable of meeting Pb-free needs, which are interlayer-connected by a low-resistance via-hole conductor having high connection reliability.

A wiring board according to one aspect of the present invention electrically connects an insulating resin layer, a plurality of wirings arranged via the insulating resin layer, and the plurality of wirings provided so as to penetrate the insulating resin layer. a wiring board having a via-hole conductors connected to the via-hole conductors comprises a metal part and a resin part including at least copper and tin and Bi, the weight ratio of the metal portion, Cu and Sn (Cu / Sn) is in the range of 1.59 to 21.43, and the metal portion is composed of three metal regions of a region made of copper (Cu) particles, a first metal region, and a second metal region, and the copper particles It is electrically connected to each other plurality of wires by contact with each other physician through the surface contact portion, a first metal region, tin (Sn), tin - copper alloys and / or tin - copper metal between compound as a main component, at least a portion of the first metal region, copper Covers the periphery so as to straddle the surface contact portions between children, second metal region is characterized that you are mainly composed of bismuth (Bi).

In addition, the method for manufacturing a wiring board according to another aspect of the present invention includes a through hole that forms a through hole by punching from the outside of the protective film into an uncured or semi-cured prepreg covered with the protective film. and forming step, a filling step of filling the via paste into the through holes, after the filling step, by peeling off the protective film, to expose the collision detecting portion partially formed to protrude in the via paste from the through-hole and more projecting Engineering that, so as to cover the protrusion, and a placement step of placing a metal foil on the surface of the prepreg, and crimping step of crimping the metallic foil to the surface of the prepreg, after the bonding step, heating at a predetermined temperature Heating step, the via paste includes Cu particles, Sn-Bi solder particles and a thermosetting resin, and the weight ratio of Cu to Sn (Cu / Sn) is 1.59 to 21 In the range of .43 Ri, in the crimping step, by a via paste is condensation pressurized pressure through the protruding portion, by touching interview Cu particles together, Toe an electrical manner connection between the metal foil, in the heating process, the compressed via paste Is heated at a temperature equal to or higher than the melting point of the Sn-Bi solder particles, and the periphery is covered with Sn-Bi solder so as to straddle the surface contact portion, and then Cu-Sn is formed around the surface contact portion so as to straddle the surface contact portion. the compound, a Bi phase in contact with the Cu-Sn compound, characterized that you generate.

The bi Apesuto for another aspect der Ru wiring board of the present invention, the wiring board, an insulating resin layer, and a plurality of wires disposed through an insulating resin layer, so as to penetrate through the insulating resin layer A via hole conductor electrically connecting a plurality of wirings provided in the via hole conductor, wherein the via hole conductor includes at least a metal part including copper, tin, and Bi, and a resin part, and the metal part includes copper (Cu ) Consisting of three metal regions, a region made of particles, a first metal region, and a second metal region, the copper particles are electrically connected to each other by contacting each other through a surface contact portion, The first metal region is mainly composed of tin (Sn), a tin-copper alloy and / or a tin-copper intermetallic compound, and at least a part of the first metal region straddles the surface contact portion between the copper particles. Covering its periphery, the second metal region is bismuth (Bi) Is obtained by the main component, via paste includes a C u particles and Sn-Bi based solder particles and a thermosetting resin, and the weight ratio of Cu and Sn (Cu / Sn) is 1.59～ The range is 21.43.

  The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

According to the present invention, the surface contact portion where the copper particles contained in the via-hole conductor of the multilayer wiring board are in surface contact forms a low- resistance conductive path, thereby realizing an interlayer connection with a low resistance value. . Moreover, it is covered with the 1st metal area | region which has a tin, a tin-copper alloy and / or a tin-copper intermetallic compound as a main component so that it may straddle the surface contact part which the copper particles surface-contacted. It is reinforced by being. Thereby, the reliability of electrical connection is improved.

1A is a schematic cross-sectional view of the multilayer wiring board 11 of the embodiment, and FIG. 1B is an enlarged schematic cross-sectional view of the vicinity of the via-hole conductor 14 in FIG. Figure 2 is an explanatory diagram for description focuses on one of the conductive paths 23 formed by a large number of copper particles 17 to touch interview. FIG. 3 is a schematic cross-sectional view showing an example of a via-hole conductor when Cu / Sn is smaller than 1.59. FIG. 4 is a process cross-sectional view for explaining an example of a method for manufacturing a multilayer wiring board. FIG. 5 shows a continuation process of FIG. 4 for explaining an example of the manufacturing method of the multilayer wiring board. FIG. 6 is a schematic cross-sectional view for explaining the multilayering of the wiring board. FIG. 7 is a schematic cross-sectional view for explaining a state when the via paste filled in the through hole of the prepreg is compressed in the embodiment. FIG. 8 is a graph showing a resistance value (1 via / mΩ) with respect to the weight ratio of Cu / Sn in the via-hole conductor obtained in the example. FIG. 9A is an electron microscope (SEM) photograph at 3000 times the cross section of the via conductor of the multilayer wiring board obtained in the example, and FIG. 9B is a trace view thereof. FIG. 10A shows an SEM photograph of 6000 times the cross section of the via conductor of the multilayer wiring board obtained in the example, and FIG. 10B shows a trace view thereof. FIG. 11A is a SEM photograph of the cross section of the via conductor of the multilayer wiring board obtained in the example, and FIG. 11B is a trace view thereof. FIG. 12A shows an image obtained by mapping the Cu element in the SEM image of FIG. 11, and FIG. 12B shows a trace diagram thereof. FIG. 13A shows an image obtained by mapping the Sn element in the SEM image of FIG. 11, and FIG. 13B shows a trace diagram thereof. FIG. 14A shows an image obtained by mapping the Bi element in the SEM image of FIG. 11, and FIG. 14B shows a trace diagram thereof. FIG. 15 is a schematic cross-sectional view for explaining a cross section of a conventional via conductor.

  An embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1A is a schematic cross-sectional view of a multilayer wiring board 11 according to the present invention. FIG. 1B is an enlarged schematic cross-sectional view of the vicinity of the via-hole conductor 14 in FIG.

  In the multilayer wiring board 11, a plurality of wirings 12 formed of a metal foil such as a copper foil are electrically connected to each other by via-hole conductors 14 that penetrate the insulating resin layer 13.

FIG. 1B is an enlarged schematic cross-sectional view near the via-hole conductor 14. In FIG. 1B, 12 is a wiring, 13 is an insulating resin layer, and 14 is a via-hole conductor. The via-hole conductor 14 includes a metal portion 15 and a resin portion 16. The metal portion 15 includes a large number of Cu particles 17, a first metal region 18 mainly composed of tin, a tin-copper alloy, and / or a tin-copper intermetallic compound, and a second metal region mainly composed of Bi. 19 is included. At least a part of the Cu particles 17, by which they form a conductive path through the surface contact portion in surface contact with each other, electricity upper wiring 12 and (12a) lower wiring 12 and (12b) Connected.

  The average particle diameter of the Cu particles 17 is preferably 0.1 to 20 μm, more preferably 1 to 10 μm. When the average particle size of the Cu particles 17 is too small, contact points increase in the via-hole conductor 14 and the conduction resistance increases. Also, particles with such a particle size tend to be expensive. On the other hand, when the average particle diameter of the Cu particles 17 is too large, the filling rate tends to be difficult to increase when the via-hole conductor 14 having a small diameter of 100 to 150 μmφ is to be formed.

  The purity of the Cu particles 17 sufficiently reduces the resistance value of the via-hole conductor 14, and more than 90% by mass in order to enable easy deformation at a portion where the plurality of Cu particles 17 are in contact with each other. Is preferably 99% by mass or more. The Cu particles 17 become softer as the purity increases. Therefore, when the purity is high, it is easy to be crushed in a pressurizing step described later, which is preferable because the contact area between the Cu particles 17 tends to be large.

  The average particle diameter of the Cu particles 17 and the contact portions 20 between the Cu particles 17 are formed by filling the formed wiring board with a resin, and then polishing the cross-section of the via-hole conductor (if necessary, fine processing such as FOCUSED ION BEAM) The sample prepared using the means is confirmed and measured by observing the sample using a scanning electron microscope (SEM).

Numerous Cu particles 17 are then touching interview each other to form a conductive path of low resistance between the wiring 12a and the wiring 12b. Therefore, the connection resistance between the wiring 12a and the wiring 12b can be reduced.

  In the via-hole conductor 14, as shown in FIG. 1B, a low resistance conduction path is formed so as to have a complicated network by randomly contacting a large number of Cu particles 17 without being regularly arranged. Has been. By forming such a network, the reliability of electrical connection can be increased. Moreover, the position where many Cu particle | grains 17 contact is random. By bringing the Cu particles 17 into contact with each other at random positions, the stress generated inside the via-hole conductor 14 when receiving heat and the external force applied from the outside can be dispersed by the deformation.

  The volume ratio of the Cu particles 17 contained in the via-hole conductor is preferably 30 to 90% by volume, and more preferably 40 to 70% by volume. If the volume ratio of the Cu particles is too low, the reliability of electrical connection by a conduction path formed by a large number of Cu particles tends to decrease. If the volume ratio is too high, the resistance value varies in the reliability test. It tends to be easy to do.

As shown in FIG. 1 (B), tin (Sn), tin - copper alloys and / or tin - at least a portion of the first metal region 18 mainly composed of copper intermetallic compound, copper grains interview touch The covered part is covered so as to straddle the surrounding area. Thus, by forming a structure such as to cover the periphery of the interview touch to that portion between the copper particles in the first metal region 18, the contact portion 20 is reinforced.

The first metal region 18 contains tin, a tin-copper alloy and / or a tin-copper intermetallic compound as a main component. Specifically, for example, Sn alone, Cu ₆ Sn ₅ , Cu ₃ Sn or the like is included as a main component. Moreover, as a remaining component, you may contain other metal elements, such as Bi and Cu, in the range which does not impair the effect of this invention, specifically, 10 mass% or less, for example.

  Further, in the metal portion 15, as shown in FIG. 1B, the second metal region 19 containing Bi as a main component does not contact the Cu particles 17 but contacts the first metal region 18. Existing. In the via-hole conductor 14, the second metal region 19 exists so as not to contact the Cu particles 17, and thus the above-described electrical influence on the via-hole conductor 14 can be suppressed.

  The second metal region contains Bi as a main component. Further, as the remaining component, an alloy of Bi and Sn, an intermetallic compound, or the like may be included in a range that does not impair the effects of the present invention, specifically, for example, in a range of 20% by mass or less.

  Since the first metal region and the second metal region are in contact with each other, both usually include both Bi and Sn. In this case, the first metal region has a higher Sn concentration than the second metal region, and the second metal region has a higher Bi concentration than the first metal region. In addition, it is preferable that the interface between the first metal region and the second metal region is unclear rather than clear. When the interface is unclear, it is possible to suppress stress concentration on the interface even under heating conditions such as a thermal shock test.

  The metal parts constituting the via-hole conductor 14 are copper particles 17, a first metal region 18 mainly composed of tin, a tin-copper alloy and / or a tin-copper intermetallic compound, and a second metal mainly composed of bismuth. And the weight ratio of Cu to Sn (Cu / Sn) is in the range of 1.59 to 21.43. The significance of this Cu / Sn ratio will be described in detail later.

  On the other hand, the resin part 16 which comprises the via-hole conductor 14 consists of hardened | cured material of curable resin. The curable resin is not particularly limited, and specifically, for example, a cured product of an epoxy resin is particularly preferable from the viewpoint of excellent heat resistance and a low coefficient of linear expansion.

  The volume ratio of the resin portion 16 in the via-hole conductor is preferably 0.1 to 50% by volume, and more preferably 0.5 to 40% by volume. When the volume ratio of the resin portion 16 is too high, the resistance value tends to be high, and when it is too low, the preparation of the conductive paste tends to be difficult during production.

Next, the effect | action of the via-hole conductor 14 in the multilayer wiring board 11 is typically demonstrated with reference to FIG.
Figure 2 is an explanatory diagram for description focuses on one of the conductive paths 23 formed by a number of Cu particles 17 with each other to touch interview. For convenience, the resin component 16 is not shown. Reference numeral 21 denotes a virtual spring shown for use in explaining the operation of the via-hole conductor 14.
As shown in FIG. 2, the conduction path is formed by a large number of Cu particles 17 randomly contacting each other, and electrically connects the wiring 12a and the wiring 12b with each other. Then, in the contact portion 20 a number of Cu particles 17 are touching interview, covering the periphery of the contact portion 20, a first metal region 18 as and straddle the contact portion 20 is formed.

  When an internal stress is generated inside the multilayer wiring board 11, an outward force is applied to the inside of the multilayer wiring board 11 as indicated by an arrow 22a. Such internal stress is generated, for example, due to a difference in coefficient of thermal expansion of materials constituting each element during solder reflow or thermal shock test.

  Such outward force is alleviated by the highly flexible Cu particles 17 themselves being deformed and the contact positions of the Cu particles 17 being somewhat displaced. At this time, since the hardness of the first metal region 18 is harder than the hardness of the Cu particles 17, the first metal region 18 tries to resist deformation of the contact portion 20. Therefore, when the contact portion 20 between the Cu particles 17 tries to follow the deformation without limitation, the contact portion 20 between the Cu particles is separated because the first metal region 18 restricts the deformation within a certain range. Until it is not deformed. This is because when the conduction path formed by contact of the Cu particles 17 is likened to a spring, if a certain amount of force is applied to the conduction path, the spring will extend to a certain extent, but the deformation follows. Is likely to increase, deformation is restricted by the hard first metal region 18. This also has the same effect when an inward force as shown by the arrow 22b is applied to the multilayer wiring board 11. Thus, the reliability of the electrical connection can be ensured by acting so as to relieve the force in any direction of the external force and the internal force as if the conduction path is the spring 21. .

  Next, in order to describe an example of a method for manufacturing a multilayer wiring board as described above, each manufacturing process will be described in detail with reference to the drawings.

  In the manufacturing method of the present embodiment, first, as shown in FIG. 4A, protective films 26 are bonded to both surfaces of the prepreg 25 in an uncured or semi-cured state (B stage).

  As the prepreg, an uncured or semi-cured (B-stage) prepreg obtained by impregnating a resin base material with a resin varnish and drying is preferably used. The fiber substrate may be woven or non-woven. Specific examples thereof include glass fiber cloth such as glass cloth, glass paper, and glass mat, and also, for example, craft paper, linter paper, natural fiber cloth, organic fiber cloth containing aramid fiber, and the like. Moreover, an epoxy resin etc. are mentioned as a resin component contained in a resin varnish. The resin varnish may further contain an inorganic filler or the like.

  Various resin films are used as the protective film. Specific examples thereof include resin films such as PET (polyethylene phthalate) and PEN (polyethylene naphthalate). The thickness of the resin film is preferably 0.5 to 50 μm, and more preferably 1 to 30 μm. In the case of such a thickness, as will be described later, a protrusion made of a sufficiently high via paste can be exposed by peeling off the protective film.

  As a method of bonding the protective film to the prepreg, when the surface of the prepreg has tackiness, the protective film can be bonded according to the tackiness.

  Next, as shown in FIG. 4B, a through hole 27 is formed by perforating the prepreg 25 provided with the protective film 26 from the outside of the protective film 26. For drilling, various methods such as drilling using a drill as well as non-contact processing methods such as carbon dioxide laser and YAG laser are used. The diameter of the through hole is 10 to 500 μm, and further about 50 to 300 μm.

Next, as shown in FIG. 4C, the via paste 28 is fully filled in the through hole 27. The via paste 28 contains Cu particles, Sn—Bi solder particles containing Sn and Bi, and a curable resin component such as an epoxy resin.
The average particle size of the Cu particles is preferably in the range of 0.1 to 20 μm, more preferably 1 to 10 μm. If the average particle size of the Cu particles is too small, it will be difficult to fill the through holes 27 with a high degree, and the cost tends to be high. On the other hand, when the average particle diameter of the Cu particles is too large, it tends to be difficult to fill the via hole conductor 14 having a small diameter.

  Moreover, the particle shape of Cu particle | grains is not specifically limited. Specifically, for example, a spherical shape, a flat shape, a polygonal shape, a scissors shape, a flake shape, or a shape having a protrusion on the surface can be given. Moreover, a primary particle may be sufficient and the secondary particle may be formed.

The Sn—Bi solder particles are not particularly limited as long as they are solder particles containing Sn and Bi. The Sn—Bi solder particles can change the eutectic point to about 138 ° C. to 232 ° C. by changing the composition ratio or adding various elements. Furthermore, wettability, fluidity, and the like can be improved by adding indium (In), silver (Ag), zinc (Zn), or the like. Among these, Sn-58Bi solder, which is a lead-free solder considering an environmental problem, having a low eutectic point of 138 ° C. is particularly preferable.
The average particle diameter of the Sn—Bi solder particles is preferably 0.1 to 20 μm, and more preferably 2 to 15 μm. If the average particle size of the Sn—Bi solder particles is too small, the specific surface area tends to be large and the surface oxide film ratio tends to be large, making it difficult to melt. On the other hand, when the average particle diameter of the Sn—Bi solder particles is too large, the filling property to the via holes tends to deteriorate.

  Specific examples of epoxy resins that are preferable curable resin components include, for example, glycidyl ether type epoxy resins, alicyclic epoxy resins, glycidyl amine type epoxy resins, glycidyl ester type epoxy resins, or other modified epoxy resins. Can do.

  Moreover, you may mix | blend a hardening | curing agent in combination with an epoxy resin. The type of the curing agent is not particularly limited, but it is particularly preferable to use a curing agent containing an amine compound having at least one hydroxyl group in the molecule. Such a curing agent acts as a curing catalyst for the epoxy resin, and also reduces the contact resistance at the time of bonding by reducing the oxide film present on the surface of the Cu particles and Sn-Bi solder particles. It is preferable from the point of having. Among these, an amine compound having a boiling point higher than the melting point of Sn—Bi solder particles is particularly preferable because it has a particularly high effect of reducing contact resistance during bonding.

  Specific examples of the amine compound include, for example, 2-methylaminoethanol (boiling point 160 ° C.), N, N diethylethanolamine (boiling point 162 ° C.), N, N dibutylethanolamine (boiling point 229 ° C.), N methylethanolamine ( Boiling point 160 ° C), N methyldiethanolamine (boiling point 247 ° C), N ethylethanolamine (boiling point 169 ° C), N butylethanolamine (boiling point 195 ° C), diisopropanolamine (boiling point 249 ° C), N, N diethylisopropanolamine ( Boiling point 125.8 ° C.), 2,2′-dimethylaminoethanol (boiling point 135 ° C.), triethanolamine and the like (boiling point 208 ° C.).

  The via paste is prepared by mixing Cu particles, Sn—Bi solder particles containing Sn and Bi, and a curable resin component such as an epoxy resin. Specifically, for example, it is prepared by adding Cu particles and Sn-Bi solder particles to a resin varnish containing an epoxy resin, a curing agent, and a predetermined amount of organic solvent, and mixing with a planetary mixer or the like. .

  The blending ratio of the curable resin component to the total amount of the metal component including the Cu particles and the Sn-Bi solder particles is in the range of 0.3 to 30% by mass, and further 3 to 20% by mass. It is preferable from the viewpoint of obtaining a low resistance value and ensuring sufficient workability.

  Moreover, as a content rate of Cu particle | grains in a metal component, it is necessary to make it contain so that the weight ratio (Cu / Sn) of Cu and Sn may become the range of 1.59-21.43. The reason for this will be described in detail later. Therefore, for example, when Sn-58Bi solder particles are used as Sn-Bi solder particles, the content ratio of Cu particles to the total amount of Cu particles and Sn-58Bi solder particles is 40 to 90% by mass, Furthermore, it is preferable that it is 55.8-65.5 mass%.

  The via paste filling method is not particularly limited. Specifically, for example, a method such as screen printing is used. In addition, in the manufacturing method of this embodiment, when filling the via hole with the via paste, when the protective film is peeled after the filling step, a part of the via paste is removed from the through hole formed in the prepreg. It is necessary to fill an amount protruding from the through hole formed in the prepreg so that the protruding portion protrudes.

  Next, as shown in FIG. 4D, by peeling off the protective film 26 from the surface of the prepreg 25, a part of the via paste 28 is protruded as a protruding portion 29 from the through hole formed in the prepreg 25. Although the height h of the protrusion part 29 is based also on the thickness of a protective film, it is 0.5-50 micrometers, for example, Furthermore, it is preferable that it is 1-30 micrometers. If the height of the protruding portion is too high, it is not preferable because the paste may press and spread on the prepreg around the through hole in the press-bonding step described later, and if it is too low, it is filled in the press-bonding step described later. There is a tendency that pressure is not sufficiently transmitted to the via paste.

Next, as shown in FIG. 5A, a Cu foil 30 is placed on the prepreg 25 and pressed in the direction indicated by the arrow. Thereby, the prepreg 25 and the Cu foil 30 are integrated as shown in FIG. In this case, since a force is applied to the protruding portion 29 through the copper foil 30 at the beginning of the press, the via paste 28 filled in the through hole of the prepreg 25 is compressed with a high force. Thereby, the interval between a plurality of Cu particles 17 is narrowed contained in via paste 28, between the Cu particles 17 touch interview.

  The pressing conditions are not particularly limited, but conditions in which the mold temperature is set from room temperature (20 ° C.) to a temperature below the melting point of the Sn—Bi solder particles are preferable. Moreover, in this press process, in order to advance hardening of a prepreg, you may use the heating press heated to the temperature required in order to advance hardening.

  Here, a state when the via paste 28 having the protrusion 29 filled in the through hole of the prepreg 25 is compressed will be described in detail with reference to FIG.

  FIG. 7 is a schematic cross-sectional view around the through hole of the prepreg 25 filled with the via paste 28. FIG. 7A shows before compression, and FIG. 7B shows after compression.

  As shown in FIG. 7 (A), the projecting portion 29 projecting from the through hole formed in the prepreg 25 is pressed through the Cu foil 30 to fill the through hole as shown in FIG. 7 (B). The via paste 28 is compressed. A part of the curable resin component 32 penetrates into the prepreg 25 due to the pressurization during the compression. As a result, the density of the Cu particles 17 and the Sn—Bi solder particles 31 filled in the through holes is increased.

  And Cu particles 17 densified in this way are in contact with each other. In compression, initially, the Cu particles 17 are in point contact with each other, and thereafter, as the pressure increases, the point contact portion is deformed and spreads, and is in surface contact. In this way, by bringing a large number of Cu particles 17 into surface contact, the upper layer wiring 12a and the lower layer wiring 12b can be electrically connected in a low resistance state. That is, according to this step, the entire surface of the Cu particles 17 is not covered with the Sn—Bi solder particles 31, and portions where the Cu particles 17 are in contact with each other can be formed. As a result, the electrical resistance of the formed conduction path can be reduced, and the surface thereof is formed so as to straddle the contact portion 20 between the Cu particles by melting the Sn—Bi solder particles 31 in the subsequent heating step. Can be covered with the first metal region 18 to form a conductive path having excellent elasticity.

Next, the compressed via paste 28 is heated at a temperature equal to or higher than the melting point of the Sn—Bi solder particles 31. The Sn—Bi solder particles 31 are melted by this heating. A first metal region 18 mainly composed of tin, a tin-copper alloy and / or a tin-copper intermetallic compound is formed around the Cu particles 17. In this case, the portion between the Cu particles 17 are touching interview is covered by the first metal region 18 so as to straddle the portion. Specifically, when the Cu particles 17 and the melted Sn—Bi solder particles 31 come into contact with each other, Sn in the Sn—Bi solder particles 31 reacts with Cu in the Cu particles 17 to form Cu ₆ Sn ₅ or A first metal region 18 mainly composed of an intermetallic compound containing Cu ₃ Sn or a tin-copper alloy is formed. On the other hand, the remaining Bi contained in the Sn—Bi-based solder particles 31 is separated from Sn and deposited, thereby forming the second metal region 19 mainly composed of bismuth (Bi).

As well-known solder materials that melt at a relatively low temperature range, there are Sn—Pb solder, Sn—In solder, Sn—Bi solder, and the like. Of these materials, In is expensive and Pb is considered to have a high environmental load.
On the other hand, the melting point of the Sn—Bi solder is 140 ° C. or lower, which is lower than a general solder reflow temperature when electronic components are surface-mounted. Therefore, when only Sn-Bi solder is used as the via hole conductor of the circuit board as a single unit, the via resistance may change due to remelting of the solder of the via hole conductor during solder reflow. On the other hand, when the via paste of this embodiment is used, Sn of the Sn—Bi solder particles reacts with the surface of the Cu particles to reduce the Sn concentration from the Sn—Bi solder particles. Through the cooling process, Bi precipitates and a Bi phase is generated. Then, by precipitating and presenting the Bi phase in this way, the solder of the via-hole conductor is not easily remelted even when subjected to solder reflow. As a result, the resistance value hardly changes even after the solder reflow.

  The temperature for heating the compressed via paste 28 is not particularly limited as long as it is a temperature not lower than the melting point of the Sn-Bi solder particles 31 and does not decompose the constituent components of the prepreg 25. Specifically, for example, when Sn-58Bi solder particles are used as the Sn—Bi solder particles, the temperature is preferably in the range of about 150 to 250 ° C., more preferably about 160 to 230 ° C. At this time, the curable resin component contained in the via paste 28 can be cured by appropriately selecting the temperature.

  In this way, a via-hole conductor is formed for interlayer connection between the upper layer wiring 12a and the lower layer wiring 12b.

  In the present embodiment, the content ratio of the Cu particles in the metal component contained in the via paste 28 is such that the weight ratio of Cu and Sn (Cu / Sn) is in the range of 1.59 to 21.43 as described above. It is necessary to contain so that it becomes. The reason for this will be described below.

  FIG. 3 is a schematic cross-sectional view showing an example of a via-hole conductor when Cu / Sn is smaller than 1.59.

As shown in FIG. 3, when the ratio of Cu / Sn is smaller than 1.59, the ratio of Cu in the via-hole conductor is reduced, so that a large number of Cu particles 17 are difficult to contact each other, and the Cu particles 17 are metal compounds. It will be scattered in a matrix of four. As a result, a large number of Cu particles 17 are hardly bound by the hard metal compound 4, so that the via-hole conductor itself is in a hard state having no spring property. Compared to the Cu particles 17, the intermetallic compound 4 such as Cu ₆ Sn ₅ and Cu ₃ Sn is hard and is not easily deformed. According to the inventors research, Vickers hardness is about 343Kg / mm ² at about 378Kg / mm ^2, Cu ₃ Sn in Cu ₆ Sn _5, significantly higher than 117 kg / mm ² for Cu.

  Since the Cu particles 17 and the intermetallic compound 4 have different coefficients of thermal expansion, internal stress due to the difference in coefficient of thermal expansion occurs during solder reflow, and as a result, cracks and voids 24 are likely to occur.

  Further, when the Cu / Sn weight ratio is smaller than 1.59, voids are more likely to occur. An important cause of the generation of such voids is Kirkendall void due to Kirkendall effect caused by contact diffusion between Sn and Cu. Kirkendall voids are likely to occur at the interface between the surface of the Cu particles and Sn or an alloy containing Sn filled in the gaps between the Cu particles.

As shown in FIG. 3, when voids or cracks exist at the interface between the Cu particles 17 and the intermetallic compound 4, the voids and cracks tend to propagate and spread easily. When a Kirkendall void occurs, the Kirkendall void also tends to propagate and easily spread. In particular, when the diameter of the via-hole conductor is small, cracks and voids tend to cause cohesive failure of the intermetallic compound 4 and further breakage of the via-hole conductor 2.
When such cohesive failure or interface failure occurs in the via-hole conductor 3, the electrical resistance of the via portion increases, which affects the reliability of the via portion.

On the other hand, the case where the ratio of Cu / Sn is 1.59 or more will be schematically described with reference to FIGS.
As shown in FIG. 1B, when the ratio of Cu / Sn is 1.59 or more, the first metal region 18 included in the metal portion 15 is physically located at a portion where a large number of Cu particles 17 are in contact with each other. Exists to protect. Arrows 22 a and 22 b shown in FIG. 2 indicate external forces applied to the via-hole conductor 2 and internal stresses generated in the via-hole conductor 2. When an external force or internal stress 22b as shown by an arrow 22a is applied to the via-hole conductor, the force is relaxed by the deformation of the flexible Cu particles 17. In addition, even if a crack occurs in the first metal region 18, a conduction path formed by the contact of a large number of Cu particles 17 is ensured, which greatly affects the electrical characteristics and reliability. Absent. As shown in FIG. 1B, since the entire metal portion 15 is elastically protected by the curable resin component 16, the deformation is further suppressed within a certain range. Therefore, cohesive failure and interface failure are less likely to occur.

Moreover, when Cu / Sn is 1.59 or more, a 1st area | region is formed in those surfaces so that the contact part of Cu particles may be straddled. That is, when Cu / Sn is 1.59 or more, the Kagen Doll void is not generated inside the Sn—Bi solder particles filled in the gaps between the Cu particles or at the interface thereof, but the copper particles. It becomes easy to generate | occur | produce in the 1st metal area | region which covers so that the circumference | surroundings of mutual contact parts may be straddled. The Kagen Doll void generated in the first metal region hardly affects the reliability and electrical characteristics of the via-hole conductor. Electrical conduction is because they are sufficiently secured by interview touch between Cu particles.

Next, as illustrated in FIG. 5C, the wiring 12 is formed. The wiring 12 is formed by forming a photoresist film on the surface of the Cu foil 30 bonded to the surface layer, patterning by selective exposure through a photomask, developing, and etching to form a Cu foil other than the wiring portion. After the selective removal, it can be formed by removing the photoresist film or the like. For the formation of the photoresist film, a liquid resist or a dry film may be used.
By such a process, a wiring substrate 41 having a circuit formed on both surfaces where the upper layer wiring 12a and the lower layer wiring 12b are interlayer-connected through the via-hole conductor 14 is obtained. By further multilayering such a wiring board 41, a multilayer wiring board 11 in which a plurality of layers of circuits are connected in layers is obtained. A method of further multilayering the wiring board 41 will be described with reference to FIG.

  First, as shown in FIG. 6A, protrusions 29 made of via paste 28 similar to those obtained in FIG. 4D are formed on both surfaces of the wiring board 41 obtained as described above. The prepreg 25 is disposed. Further, a Cu foil 30 is arranged on each outer surface of each prepreg 25 to form an overlapped body. And this laminated body is inserted | pinched between a press metal mold | die, and a laminated body as shown in FIG.6 (B) is obtained by pressing and heating on the conditions as mentioned above. Then, a new wiring 42 is formed by using the photo process as described above. In this way, further multilayering can be achieved. By repeating such a multilayering process, further multilayering is possible.

  Next, the present invention will be described more specifically with reference to examples. The scope of the present invention is not construed as being limited in any way by the contents of this embodiment.

First, the raw materials used in this example will be described together below.
Cu particles: 1100Y manufactured by Mitsui Metals, Ltd. with an average particle size of 5 μm
・ Sn-Bi solder particles: Sn42-Bi58, average particle size 5 μm, melting point 138 ° C., manufactured by Yamaishi Metal Co., Ltd./Epoxy resin: jeR871 manufactured by Japan Epoxy Resin Co., Ltd.
・ Curing agent 1: 2-methylaminoethanol, boiling point 160 ° C., manufactured by Nippon Emulsifier Co., Ltd. ・ Curing agent 2: amine adduct type curing agent (solid), melting point 120-140 ° C., manufactured by Ajinomoto Fine Techno Co., Ltd. Curing agent 3: 2,2'-dimethylaminoethanol, boiling point 135 ° C
・ Prepreg: 500 mm long x 500 mm wide, 100 μm thick, glass fiber substrate impregnated with epoxy resin)
・ Protective film: 25 μm thick PET sheet)
・ Copper foil (thickness 25μm)

(Adjustment of via paste)
Via paste was prepared by blending Cu particles, Sn-Bi solder particles, epoxy resin, and curing agent in the blending ratio shown in Table 1 and mixing with a planetary mixer.

(Manufacture of wiring boards)
A protective film was bonded to both surfaces of the prepreg. Then, 100 or more holes having a diameter of 150 μm were drilled from the outside of the prepreg bonded with the protective film with a laser.
Next, the prepared via paste was fully filled in the through holes. And the protrusion part in which a part of via paste protruded from the through-hole was exposed by peeling the protective film of both surfaces.
Next, copper foil was arranged on both surfaces of the prepreg so as to cover the protrusions. Then, a prepreg on which a copper foil is placed is placed on the lower mold of a pair of molds of a heating press through a release paper, and the temperature is raised from room temperature 25 degrees to a maximum temperature 220 degrees C in 60 minutes. The temperature was kept at 220 ° C. for 60 minutes, and then cooled to room temperature over 60 minutes. The press pressure was 3 MPa.

(Evaluation)
<Resistance test>
The resistance value of 100 via-hole conductors formed on the wiring board was determined by measuring by the 4-terminal method. Then, 100 average resistance values and maximum resistance values were obtained. A case where the maximum resistance value was less than 2 mΩ was determined as A, a case where the maximum resistance value was 2 to 3 mΩ was determined as B, and a case where the maximum resistance value was greater than 3 mΩ was determined as C. When the maximum resistance value is small, it can be said that the standard deviation σ of the resistance value is also small.
<Peel test>
The adhesion of the via-hole conductor when the copper foil on the surface of the obtained wiring board was peeled (or destroyed) was examined. At this time, it was judged as A when it was not peeled, B when it was difficult to peel, and C when peeled easily.
<Initial resistance value>
The connection resistance value of 100 via holes formed on the wiring board was measured by the 4-terminal method. In addition, as an initial resistance value, 1 A or less was determined as A, 1 Ω or less and 1 Ω exceeding 1 Ω were mixed as B, and all exceeding 1 Ω were determined as C.
<Connection reliability>
A heat cycle test of 500 cycles of the wiring substrate on which the initial resistance value was measured was performed, and when the rate of change with respect to the initial resistance value was 10% or less, A was determined to be A when it exceeded 10%.
The results are shown in Table 1. Moreover, the graph which plotted the average resistance value with respect to the mass ratio of Cu / Sn is shown in FIG.

  From the graph of FIG. 8, it can be seen that the resistance value sharply decreases from the Cu / Sn weight ratio of around 1.59, and from around 3. This seems to be because the contact ratio between the Cu particles is increased by increasing the ratio of the Cu particles 17. That is, it is considered that there is almost no metal having a higher resistance value than Cu between adjacent Cu particles 17 and Cu particles 17.

  In other words, when the resistance value is less than Cu / Sn 1.59 where the resistance value increases abruptly, it is considered that a metal having a high resistance value is interposed between the many Cu particles 17.

  Also, from Table 1, when the ratio of Sn42-58Bi particles is 60% by mass or less, the average resistance value and the maximum resistance value are 3 mΩ or less, and when it is 44.2% by mass or less, it is extremely small as 2 mΩ or less. I understand. However, it can be seen that exfoliation is likely to occur when Sn42-58Bi particles are not contained. On the other hand, it can be seen that exfoliation hardly occurs as the proportion of Sn42-58Bi particles increases.

It can also be seen that both low resistance and high reliability can be achieved when the ratio of Sn42-58Bi particles is in the range of 10 to 60% by mass. If the proportion of Sn42-58Bi particles is too low, the connection reliability is insufficient to first metal region present around the contact portions Cu particles each other to touch interview is reduced. On the other hand, when the ratio of Sn42-58Bi particles is too high, the first metal region is excessively increased, so that the number of contact portions where the Cu particles are in contact with each other is decreased, thereby increasing the resistance value.

  Also, paste No. When the multilayer wiring boards obtained using 7 to 9 are compared, paste No. 7 whose boiling point of the curing agent is higher than the melting point 138 ° C. of Sn42-58Bi particles. 7, no. In the case of 8, it can be seen that the balance of resistance reduction and high reliability is more excellent. When the boiling point is low, the oxide layer on the surface of the solder is reduced, and the volatilization of the curing agent starts before melting, so that the metal part area becomes small, which causes a problem in connection reliability of the via hole. The boiling point of the curing agent is desirably 300 ° C. or lower. When it is higher than 300 ° C., the curing agent becomes special and may affect the reactivity.

  Here, typically, paste No. 1 according to the present invention is used. 9 to 10 show an electron microscope (SEM) photograph of a cross section of the via conductor of the multilayer wiring board obtained using 6 and a trace view thereof. Note that FIG. 9 is 3000 times and FIG. 10 is 6000 times, and shows an SEM photograph (A) and a trace view (B) thereof, respectively. Further, FIG. 11 shows an SEM photograph and a trace view of a cross section of a via conductor used in EPMA (Electron Probe Micro Analyzer).

From 9 to 11, the resulting via hole conductor a number of Cu particles 17 are highly filled, it can be seen that the touch interview each other. Thereby, it turns out that a conduction path with a low resistance value is formed. The portion between the Cu particles 17 are touching interview, so as to straddle the contact portion, tin (Sn) or tin - copper intermetallic compound or tin - first metal regions 18 mainly composed of copper alloy It can be seen that it is formed. Moreover, it turns out that the 2nd metal area | region 19 which has Bi with a high resistance value as a main component is not substantially in contact with Cu particle | grains. In this second metal region, it is considered that Sn in the Sn42-58Bi particles forms an alloy (for example, an intermetallic compound) with Cu on the surface of the Cu particles 17, so that a high concentration of Bi is precipitated.

  FIG. 12 shows an image (A) when the SEM image of FIG. 11 is mapped with Cu element by EPMA and a trace view (B) thereof.

  12 (A) and 12 (B), it can be seen that a large number of Cu particles are present at high density and randomly in the obtained via-hole conductor. Moreover, it turns out that many Cu particle | grains are electrically connected by contacting directly.

  FIG. 13 shows a mapping image (A) of the Sn element using the SEM image of FIG. 11 and a trace diagram (B) thereof.

  13A and 13B, it can be seen that the first metal region 18 is formed on the surface of the contact portion where a large number of Cu particles are in direct contact with each other so as to straddle the contact portion.

  In FIG. 13, it seems that most of the surface of the Cu particles is covered with the first metal region. However, since the epoxy resin permeates in EPMA, not only the Sn element on the surface of the observation surface but also the Sn element on the base is detected. Therefore, actually, the first metal region does not cover most of the surface of the Cu particles, but exists so as to straddle the contact portion. This can also be seen from the SEM images shown in FIGS. According to such a structure, the stress generated in the relatively hard first metal region is absorbed by the soft Cu particles 17. For this reason, it is possible to prevent the crack generated in the first metal region from propagating and spreading.

  Further, FIG. 14 shows a mapping image (A) of the Bi element using the SEM image of FIG. 11 and a trace diagram (B) thereof.

  From FIG. 14, it can be seen that Bi exists so that the second metal region does not come into contact with the Cu particles. From this, it can be seen that Bi having a high resistance value does not affect the conduction path formed by the contact of the Cu particles.

  According to the present invention, it is possible to further reduce the cost, size, function, and reliability of a multilayer wiring board used for a mobile phone or the like. Also, from the via paste side, by proposing an optimum material for forming a via paste with a reduced diameter via paste, it contributes to the miniaturization and high reliability of the multilayer wiring board.

DESCRIPTION OF SYMBOLS 11 Wiring board 12 Wiring 13 Insulation resin layer 14 Via hole conductor 15 Metal part 16 Resin part 17 Cu particle 18 1st metal area 19 2nd metal area 20 Contact part 21 Spring 24 Void 25 Prepreg 26 Protective film 27 Through-hole 28 Via paste 29 Protrusion 30 Cu foil 31 Sn-Bi solder particles

Claims (12)

An insulating resin layer; a plurality of wirings arranged via the insulating resin layer; and a via-hole conductor that electrically connects the plurality of wirings provided so as to penetrate the insulating resin layer. A wiring board,
The via-hole conductor includes a metal portion and a resin portion,
The metal part is
A first metal region mainly composed of copper (Cu) particles, tin (Sn), tin-copper alloy and / or tin-copper intermetallic compound, and a second metal region mainly composed of bismuth (Bi). And the weight ratio of Cu and Sn (Cu / Sn) is in the range of 1.59 to 21.43,
The copper particles electrically connect the plurality of wirings by contacting each other, and at least a part of the first metal region straddles a portion where the copper particles are in contact with each other. A wiring board characterized by covering the periphery of the wiring board.   The wiring board according to claim 1, wherein the second metal region is not in contact with the copper particles in the metal portion.   The wiring board according to claim 1 or 2, wherein a volume ratio of the copper particles in the via-hole conductor is 30 to 90%. A through-hole forming step of forming a through-hole by piercing from the outside of the protective film in an uncured or semi-cured prepreg coated with a protective film;
A filling step of filling the through hole with via paste;
After the filling step, by peeling off the protective film, a peeling step of exposing a protruding portion formed by protruding a part of the via paste from the through hole, and
An arrangement step of arranging a metal foil on the surface of the prepreg so as to cover the protruding portion,
A crimping step of crimping the metal foil to the surface of the prepreg;
A heating step of heating at a predetermined temperature after the crimping step,
The via paste includes Cu particles, Sn-Bi solder particles, and a thermosetting resin, and a weight ratio of Cu to Sn (Cu / Sn) is in a range of 1.59 to 21.43. ,
In the crimping step, by compressing the via paste through the protruding portion, the Cu particles are brought into contact with each other and electrically connected to each other,
In the heating step, heating is performed at a temperature equal to or higher than the melting point of the Sn—Bi solder particles.   The method for manufacturing a wiring board according to claim 4, wherein the thermosetting resin is an epoxy resin.   The said epoxy resin is a manufacturing method of the wiring board of Claim 5 containing the hardening | curing agent which is an amine compound which has an at least 1 or more hydroxyl group in a molecule | numerator.   The method for manufacturing a wiring board according to claim 6, wherein the boiling point of the amine compound is not less than the melting point of the Sn—Bi solder particles and not more than 300 ° C. 7.   It contains Cu particles, Sn-Bi solder particles, and a thermosetting resin, and the weight ratio of Cu to Sn (Cu / Sn) is in the range of 1.59 to 21.43. Via paste.   The content ratio of the Cu particles with respect to the total amount of the Cu particles and the Sn-Bi solder particles is 40 to 90 mass%, and the content ratio of the Sn-Bi solder particles is 10 to 60 mass%. The via paste according to claim 8.   The via paste according to claim 8 or 9, wherein the thermosetting resin is an epoxy resin.   The via paste according to claim 10, wherein the epoxy resin contains a curing agent that is an amine compound having at least one hydroxyl group in a molecule.   The via paste according to claim 11, wherein the amine compound has a boiling point not lower than the melting point of the Sn—Bi solder particles and not higher than 300 ° C.